[Britwrench]

Sounds like a fuel pressure or injector problem. Listen to the injectors with a stethescope while someone else cranks the engine. They should sound the same. Then you need to check the fuel pressure from cold.
If you have a infra-red temp non-contact
tester, check the exhaust temps on each cylinder to see if it really is only firing on three. If lost go to shop for help.